The invention relates to a method and an arrangement for setting data transfer parameters in a data transfer system. The invention is applied preferably in a digital cellular system for changing a channel configuration during a connection.
In digital cellular systems the connection parameters are generally set in the context of the establishment of a data transfer connection before the data transfer connection intended for the transfer of user information is established. For example in a GSM (Global System for Mobile Communications) system connection parameters of this kind are amongst others a codec which defines a data transfer rate coding and parameters defining speech data and fax transfer functions. Codecs currently in use are HR (Half Rate). FR (Full Rate) and EFR (Enhanced Full Rate) codecs. Of these the FR codec can be selected according to the GSM system standard for all devices connected to the system but the HR and EFR codecs are optional in the devices. Connection parameters of a data link contain amongst others specifications concerning bits and bytes to be transferred. In the following first a prior known procedure is described for setting connection parameters in a GSM system and thereafter the disadvantages associated with the prior art.
Prior to the establishment of a data transfer connection a message for the establishment of the connection is transmitted from a mobile station to the data transfer system and it contains data concerning capabilities of devices for data transfer in BC (Bearer Capability) data fields reserved for this purpose. When the mobile station has transmitted the message concerned to the data transfer system the data system verifies the compatibility of the parameters contained in the message. Thereafter, the system transmits an acknowledge message to the mobile station confirming the reception of the message establishing the connection and the data concerning whether the suggested parameters are compatible. In case that the suggested parameters are not compatible it is possible to negotiate the parameters and change some of the parameters by transmitting new parameters in the acknowledge message.
In a BC data field, one can, for example, state that the terminal is capable of data transfer at the HR and FR data transfer rate. Then during the connection the data transfer system uses one of the data transfer rates concerned. The data transfer rate can be changed during the connection, for example, in the context of a change from one base station to the next (handover). Then, for example, those base stations which are capable of using the HR data transfer rate use it and the other base stations use the FR data transfer rate. The change of a codec occurs then controlled by the data transfer system within the framework of the BC data in use. The change of the codec is implemented by using a so-called ASSIGNMENT or HO (Handover) procedure.
In addition, a procedure for alternating speech connection and data connection is prior known. In this case, the message for establishing a connection to be transmitted during the establishment of connection contains two BC data fields. Of these, for example, the first data field BC1 is used for the configuration of the speech connection and the data field BC2 is used for the configuration of the data connection. During the connection the configuration in use can be changed between configurations BC1 and BC2 which were specified during the establishment of the connection. This change occurs by using a so-called ICM (In Call Modification) procedure.
The GSM system has been described in more detail, for example, in the publication [1] Mouly, Pautet; The GSM System for Mobile Communications 1992. ISBN 2-9507190-0-7.
There are many disadvantages associated with the solutions according to the prior art described above. First, a connection which has been set up as a plain speech connection cannot be converted to a data connection during the connection. If during a speech connection there arises a need, for example, to send a fax the speech connection has to be disconnected and a new connection established which is configured for a fax transfer in the stage of the establishment of connection. Although the need for several channel configurations would be known already at the establishment of connection, it is not possible to use more than two sets of connection parameters during the same connection in the solutions according to the prior art. Thus, for example, during a speech/data connection one cannot send faxes. Instead one must establish a new connection to perform this task.
Another disadvantage associated with the prior art is that one has to know the parameters of the data transfer connection already at the establishment of connection. If, for example, the device configuration of a terminal may vary parameters relating to the wrong device configuration may be selected when the connection is established, in which case the connection has to be established again for the correction of the parameters. Such a situation may arise especially for the reason that the peripheral attached to the terminal is not connected when the connection is established and the system reports this only after the connection has been established.
Problems arise especially in a situation where the appropriate data transfer parameters are not known at the establishment of connection but they have to be found out by trial and error. During this procedure, one has to establish many speech connections to agree on the trial parameters with the other party and many data connection trials for testing the agreed trial parameters.
Additionally, the use of the solutions according to the prior art is made difficult by the fact that separate subscriber numbers are usually required for speech, data and fax functions and for their transposition functions.
As is obvious from the above described examples, the procedure according to the prior art is in many operating situations multi-stage and awkward and therefore the total time needed for transferring the necessary data may become unreasonably prolonged.
One idea of the invention is that a procedure is devised for setting connection parameters during the data transfer connection. Then it is possible to change the channel configuration of the connection when necessary, independent of the configuration selected at the establishment of connection.
By means of the invention, many advantages are achieved compared to the prior art. By means of the solution according to the invention, data transfer connection can be established by setting first, for example, connection parameters relating to the speech connection and during the speech connection the connection parameters can be chanced so that they are suitable for data transfer when necessary. Thus, at the call setup, no information is needed on whether the data transfer connection will possibly be used for data and/or fax transfer nor information on the parameters to be used in this kind of transfer. During speech connection it is also possible to find out the operation of different data transfer parameters in the context of the terminals in use. Furthermore one advantage of the invention is that separate subscriber numbers needed for speech fax and data transfer functions and their transposition functions (multiple nubering scheme) can be substituted by a single subscriber number (single numbering scheme). Thus the invention makes the single numbering scheme a viable solution.
A method according to the invention for setting data transfer connection parameters in a data transfer system is characterized in that the connection parameters which are to be used in the data transfer connection are selected after the establishment of the data transfer connection data referring to the selected connection parameters is transferred between the terminal and the data transfer system and the connection parameters used by the data transfer connection are changed to be compatible with the transferred connection parameters.
A data transfer system according to the invention comprising the means for transferring the first connection parameters between said data transfer system and a terminal connected to it and the means for establishing data transfer connection on a traffic channel on the basis of said first connection parameters is characterized in that it comprises the means for transferring the second connection parameters between said data transfer system and said terminal during said data transfer connection and the means for changing the connection parameters used in said data transfer connection on the basis of said second data transfer parameters.
A terminal according to the invention comprising the means for transferring the first data transfer parameters between the terminal and the data transfer system and the means for establishing data transfer connection to the data transfer system on the basis of said first data transfer parameters is characterized in that the terminal comprises the means for transferring the second data transfer parameters between the terminal and the data transfer system during said data transfer connection and the means for changing the connection parameters used in said data transfer connection on the basis of said second data transfer parameters.
Preferable embodiments of the invention have been presented in dependent claims.